Determine acid-base transporters in duodenal enterocytes of healthy human volunteers, determine if a defect is present in acid-base transport and regulation of pHi in duodenal epithelia of patients with duodenal ulcer disease, and study the effect of eradication of helicobacter pylori on acid-base transport mechanisms in duodenal epithelia of patients with duodenal ulcer disease. Identify the cellular abnormalities in acid/base transport in patients with cystic fibrosis.